Three separate categories of prior art exit which constitute relevant background to the invention.
The first category of prior art is concerned with switches comprising only one displaceable optical element facing a plurality of fixed output ports. Many examples of this category of switches exist, for example: U.S. Pat. No. 6,335,993B1 (Takahashi) where the single mobile collimator is fixed to a disc rotating about its central axis; U.S. Pat. No. 4,896,935 (Lee) where a single displaceable collimator is rotatable to point towards a series of radially extending collimators; and U.S. Pat. No. 657,339 (Fick) where a single displaceable fibre through a contraction of a 1 dimensional piezoelectric arrangement allows the fibre to bend in between two positions where fixed fibres are located. Other examples in this category may be structures with a single fixed input port and multiple fixed output port with a single optical element displaced to achieve switching such as JP2004287124 (Nin Sensho) and CA200223 86309 (Sun De-Gui).
A second category of prior art exists which shows multiple input and output switches with a number of actuators equaling the total number of ports. In other words, these often require the input and the output ports to be displaceable for switching to occur. WOO 1/50176 (Polatis) and U.S. Pat. No. 6,005,998 (Lee) both show at least one actuator per port. In other words, for a total of M+N ports, there are provided at least M+N actuators to displace optical elements. U.S. Pat. No. 6,859,120 (Sweatt William et al) also shows a system using actuators on both the input side and the output side of an optical switch.
A third category of switches relies on the use of at least two displaceable optical elements between fixed arrays of input and output ports. For example, U.S. Pat. No. 6,456,751B1 (Bowers et al) shows the use of two micro-actuated arrays of mirrors. Another example can be found in JP2001350105 where a series of at least two moveable prisms is envisaged to switch a beam from one port to another in a multiple input and multiple output switch. This category of switches also requires at least the same number of actuated optical elements as their total number of ports.
Due to their large number of ports and requirement for a large number of actuators, these switches are therefore unnecessarily bulky requiring a large number of expensive actuators which will also need precise control.